1. Field of the Invention
The present invention relates generally to a semiconductor packaging technique, and more particularly to a memory card and method for fabricating the same.
2. Description of Related Art
With the increasing development of digital products such as cameras, mobile phones, PDAs (Personal Digital Assistants), video and audio players, demands for flash memory cards are increasing. The flash memory cards are generally categorized into CF (Compact Flash) cards, SMCs (Smart Media Cards), MMCs (Multi Media Cards), SD (Secure Digital) cards, MS (Memory Stick) cards and so on. While the storage capacity of the memory cards keeps growing, structure of the memory cards is continuously improved so as to prevent easy breaking of the memory cards and meanwhile allow the memory cards to obtain a desired waterproof effect.
A conventional memory card generally comprises two sheets with a circuit board disposed therebetween. The two sheets are bonded together by using a high frequency welding technique, thereby forming a memory card structure. However, the memory card can easily break or be damaged from the bonding position or tiny spacing can appear at the bonding position after many times the memory card is inserted into and taken out from an electronic product over a long period of time. Techniques related to the memory card structure are disclosed by such as U.S. Pat. Nos. 5,677,524, 6,040,622, 6,624,005 and Japan Patent No. 62-239554.
Taiwan Patent No. 570294 discloses a method for fabricating a memory card, which comprises disposing and electrically connecting chips to a plurality of circuit board units of a circuit board; forming an encapsulant on the circuit board; cutting between the circuit board units by using a grinding wheel cutter so as to obtain a plurality of rectangle shaped packages in batch type; and embedding each package into a housing. However, the need of the housing and adhering the housing to the package increase cost and complicate the fabricating process, which cannot meet economic efficiency.
In addition, with development of much thinner, lighter, shorter and smaller electronic devices, memory cards are required to be further reduced in size, which has developed from MMC to RS-MMC (Reduced Size Multi Media Card) and MMC-Micro and developed from SD to mini SD and Micro-SD. Sony Corporation further develops Memory Stick Micro (M2). Corresponding to variation of fabricating processes and products, shape of memory cards is not any more limited to the conventional rectangular shape, but may be in any irregular shape. However, the above-described grinding wheel cutter can only form straight line cutting path and accordingly cannot meet demand of card type packages in irregular shape such as Micro-SD, MMC-Micro and M2.
U.S. Pat. No. 6,548,911 discloses a MMC fabricating technique eliminating the need of the housing. However, the technique can only be used to fabricate MMC type memory cards and cannot be used to fabricate memory cards of irregular shape such as MMC-Micro and Micro-SD.
US Patent Publication No. 2004/0259291 discloses a fabricating technique that can fabricate memory card packages in irregular shape and eliminate the need of the housing. The technique mainly comprises performing chip mounting and wire bonding processes corresponding to a plurality of circuit board units on a circuit board; forming an encapsulant on the circuit board; cutting the package by grinding, water jet or laser so as to form a plurality of card type packages in irregular shape such as Micro-SD, MMC-Micro and M2.
However, in the above-described fabricating process, the water jet used for cutting the packages of irregular shape involves making the water pass through ultra high pressure booster so as to increase water pressure to 55000 psi and then emitting the water from a nozzle having a diameter of 0.004 inch, thereby generating a high speed water stream of 3000 feet per second (about three times the sound speed). Meanwhile, fine sand of high rigidity can be added to increase the cutting ability for cutting metal or rigid material. But the water jet process needs high cost. Also, since an abrasive material of fine sand needs to be added to the water column of the water jet, the powder and the slag generated by the fine sand pollute the environment. Also, because the abrasive material must be discarded after one time use and cannot be recycled, the fabricating cost is relatively high. Further, as the cutting width and cutting path of the water jet are limited by pressure of the water jet and size of particles of the abrasive material, during cutting irregular packages, the cutting path can be unstable, which can adversely affect the fabricating yield. Further, the nozzle of the water jet may sometimes be blocked by the abrasive material, which relatively increases instability of the process. Moreover, as the cutting surface is often washed by the fine sand, it can become uneven.
Accordingly, a laser cut is tried to overcome the above drawbacks. However, the laser cut can lead to burning of the encapsulant and periphery of the circuit board, and result in an uneven cutting surface. Meanwhile, the laser cut can cause such problems as burr cuts and powder pollution. In addition, limited by the laser irradiation angle, part of the cutting surface of the package can become inclined. Also, the laser cutting cost (such as laser cutting equipment and lamp cost) is too high and cannot meet economic efficiency. Moreover, both the water jet and laser cutting can result in chip-out or cracking of the encapsulant when cutting from the upper side of encapsulant downward using fine sand or energized beam, thereby adversely affecting the shape and quality of the memory card packages.
Therefore, there is a need to provide a memory card and method for fabricating the same, which eliminates the need to perform a shape cutting process, has simplified fabricating process, shortened fabricating time, improved fabricating yield and low fabricating cost.